1. Field of the Invention
The present invention relates to a manufacturing method for a coated-type magnetic recording medium.
2. Discussion of Background
Magnetic recording media of this type are manufactured by a process in which the magnetic layer is formed on a flexible support. The methods for forming magnetic layers in the known art include the coating method, the vapor deposition method and the sputtering method.
The thickness of the magnetic layer, backcoating and the like in a coated-type magnetic recording medium is normally within the range of 0.3 .mu.m to 4.0 .mu.m. The wet layer thickness of a coating in this range at the time of application will be approximately 2 .mu.m to 40 .mu.m. When forming such a coated layer with a stationary-type coating method using a stationary coating device such as a nozzle, foreign matter may be present that exceeds the size of the gap between the coating device and the flexible support, which is formed from polyester films such as PET (polyethylene terephthalate) or PEN (polyethylene naphthalate), or an alamid film. Such foreign matter can become caught in the coating device causing striations in the coating. Even when it does not result in coating striations, the foreign matter may-become a cause of drop-out. Therefore, in order to improve the quality of the product and the yield at the time of manufacturing, measures for removing foreign matter are of critical importance.
Also, with the vapor deposition and sputtering methods used to make the magnetic layer extremely thin and the recording density high, even minute particles of foreign matter will result in coating defects or drop-out. The foreign matter that is present on the flexible support may be introduced during production of the flexible support and may, therefore, already be present when it is delivered to the user, or the flexible support may be contaminated with foreign matter at the user's facility before the magnetic layer is formed. The composition of such foreign matter includes dust, human tissue such as dandruff, fibers and particles resulting from abrasion of the facilities.
In order to improve the quality of their products and to improve the production yield, and in particular in order to improve product quality and yield of products manufactured with methods such as stationary coating that are especially vulnerable to foreign matter, manufacturers of magnetic recording media have been looking for ways to remove any and all foreign matter from the flexible support before forming the magnetic layer, and various methods of cleaning have been tried. However, the rate at which coating striations occur is much higher in the stationary-type coating methods, compared with coating methods that utilize rotary bodies such as the reverse roll coating method and the gravure cylinder coating method. The present situation is, nevertheless, that a satisfactory result has not yet been obtained with the means for cleaning in the known art. The means for cleaning in the known art include the washing method, the wiping method using an unwoven cloth or the like, ionized air blowing and vacuum cleaning. Of these, the washing method, for example, provides good cleaning effect but with this method it is difficult to support high-speed in-line continuous cleaning, or to use it in a vacuum used in magnetic layer forming methods with vapor deposition, sputtering or the like. It is also difficult to handle situations in which there is a functional layer such as a magnetic layer, a non-magnetic layer or the like, already formed on one side. The wiping method, using an unwoven cloth or a woven cloth, presents such problems as exchange of foreign matter, as bits and pieces of the cloth tend to adhere to the layer. The ionized air blowing and vacuum cleaning methods do not provide a perfect effect in removing foreign matter either. Therefore, currently, two or more of these methods are combined to achieve the best possible result in removing foreign matter, which is still less than satisfactory.